Mitosis is the process of cell division that results in two genetically identical daughter cells from a single parent cell. The steps of mitosis, in order, are as follows:
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Prophase:
- Chromatin condenses into visible chromosomes, each consisting of two sister chromatids joined at the centromere.
- The nuclear membrane begins to break down.
- The mitotic spindle starts to form from the centrosomes, which move to opposite poles of the cell.
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Prometaphase:
- The nuclear envelope completely disintegrates.
- Microtubules from the spindle attach to the kinetochores (protein structures on the centromeres) of the chromosomes.
- Chromosomes begin moving toward the center of the cell (the metaphase plate).
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Metaphase:
- Chromosomes are aligned along the metaphase plate in the center of the cell.
- The spindle assembly checkpoint ensures that all chromosomes are properly attached to the spindle apparatus.
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Anaphase:
- Sister chromatids are pulled apart as the centromeres split.
- The spindle fibers shorten, pulling the separated chromatids (now individual chromosomes) toward opposite poles of the cell.
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Telophase:
- Chromosomes reach the opposite poles and begin to de-condense back into chromatin.
- The nuclear envelope re-forms around each set of chromosomes, resulting in two nuclei within the cell.
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Cytokinesis (though technically not a part of mitosis, it usually occurs concurrently):
- The cytoplasm divides, leading to the formation of two separate daughter cells. In animal cells, this is achieved through a cleavage furrow, while in plant cells, a cell plate forms to separate the two new cells.
These steps ensure that the genetic material is accurately duplicated and distributed to the daughter cells.